The present invention relates to transgenic plants and their preparation.
Phosphofructokinase (PFK; EC 2.7.1.11) is widely regarded as a key regulatory enzyme controlling the entry of carbon into glycolysis. Glycolysis, especially in plant cells, serves to supply both respiratory carbon for energy production and intermediates for other metabolic pathways. The potato tuber contains four forms of PFK (Kruger et al., Arch. Biochem. Biophys. 267:690-700) and pyrophosphate fructose-6-phosphate phosphotransferase (PFP; EC 2.7.1.90) which can catalyze the conversion of fructose-6-phosphate to fructose-6-bisphosphate. PFK is present in both the cytosol and the amyloplast while PFP is only known to occur in the cytosol.
It has previously been thought that PFK alone controls the total glycolytic flux. However, we have now found that this is not the case. We introduced additional PFK into potato plants by genetic manipulation. Our results indicate that a substantial increase in PFK activity did not substantially alter flux through glycolysis but changed the pool sizes of intermediates. The results indicate that regulation of glycolytic flux may be achieved not only at the entry of carbon into the pathway but also exit from it. This finding has general applicability.
Accordingly, the present invention provides a process for the preparation of a transgenic plant, which method comprises:
(i) transforming a plant cell with a chimeric gene comprising (a) a suitable promoter and (b) a coding sequence the product of which causes modification of the amount of metabolic intermediate in glycolysis or in a pathway for the synthesis or degradation of starch, sucrose or reducing sugar; and
(ii) regenerating a plant from the transformed cell.
The invention also provides the chimeric gene. A vector suitable for use in the present process comprises the chimeric gene such that the chimeric gene is capable of being expressed in a plant cell transformed with a vector. A plant cell according to the invention therefore harbors the chimeric gene such that the chimeric gene is capable of being expressed therein.
A transgenic plant can therefore be obtained which harbors in its cells the chimeric gene such that the chimeric gene is capable of being expressed in the cells of the plant. Seed or other propagules can be obtained from the transgenic plant and used to grow further plants stably transformed with the chimeric gene.